Cosmic Radiation Makes Trees Grow Faster 162
Diamonddavej writes "The BBC reports that researchers at the University of Edinburgh have found that Galactic Cosmic Rays (GCRs) somehow makes trees grow faster. GCRs vary according to the 11-year solar cycle, with more GCRs hitting the Earth during solar minimum when there is a lull in the solar wind, which normally acts to protect the inner solar system from external galactic radiation. The mechanism might have something to do with GCRs increasing cloud cover, which diffuses sunlight and increases the efficiency of photosynthesis. Nevertheless, the researchers remain mystified and are requesting further ideas and research collaboration to test hypotheses. (How about Radiation Hormesis, AKA 'Vitamin-R?')" Here is the paper's abstract at the journal New Phytologist. The researchers say: "The relation of the rings to the solar cycle was much stronger than to any climatological factors. ... As for the mechanism, we are puzzled."
causality is possibly wrong (Score:5, Interesting)
If the solar cycle is what determines the level of GCR that gets to Earth then it may very well have absolutely nothing to do with the tree growth its self but an indicator of solar conditions which influence tree growth rates.
Cloud cover (Score:5, Interesting)
The mechanism might have something to do with GCRs increasing cloud cover, which diffuses sunlight and increases the efficiency of photosynthesis.
How about cloud cover leads to more precipitation?
Re:causality is possibly wrong (Score:4, Interesting)
That's what I'm thinking too. GCR intensity is highest when sunspot activity is lowest, generally modulating on an 11 year [nature.com] cycle. But solar irradiance also varies at the same frequency; the Sun is actually (~0.1%) brighter when more sunspots are present, contrary to intuition.
If tree growth between 1953-2006 really is highest when sunspot activity is lowest, that implies trees grow faster when the Sun is very slightly dimmer. Weird. Their diffusion explanation makes sense, but as they note this cloud condensation effect is supposed to be a very small effect. Perhaps it's just large enough to be noticed in these proxy data, though. I agree, however, that a link to solar irradiance is more intuitively appealing, and it's not immediately obvious how it could be ruled out.
I'd bet they've already considered this issue and ruled it out, possibly by using satellite measurements of solar irradiance and solar wind over the last few decades. They're supposed to be tightly correlated, but if the solar wind varies even slightly differently than solar irradiance it should be possible to see which is causing this variation in growth rates.
Re:Cloud cover (Score:3, Interesting)
Yeah well it depends on where you are. Here in Australia getting water vapor to precipitate before it crosses the east coast is an issue. Most of it flies right over because we don't have enough terrain to push it up to form ice.
Re:Nitrogen Fixation (Score:4, Interesting)
Only lightning and cosmic rays can form nitrogen oxide, and lightning is relatively rare,
Well no, lighting is fairly common, actually -- there's always a lighting storm going on somewhere. However, if one assumes that the global rate of lightning is fairly constant then given that the amount nitrogen oxides contributed by cosmic rays fluctuates, you'd still see a correlation. So you may be right.
Re:Nitrogen Fixation (Score:1, Interesting)
Do we get to see your data now, or do we have to wait for your upcoming paper in The New Phytologist as well?
Complex Systems + Causality ... (Score:3, Interesting)
Keeping that in mind, I tend to be of the opinion that the best guess regarding an isolated cause is '42'.
CC.
Sun spots (Score:3, Interesting)
At the university I studied physics at, they had a nice (old) telescope with which they projected solar images to count sun spots. They had a graph on the wall of the number of sun spots, going decades back. There was a nice periodicity in that graphc, and interesting thing is that they could point out two types of events: good wine years, and the occurrence of the "Elfstedentocht" (a major Dutch ice skating event which only happens when the outdoor ice conditions are exactly right).
I forgot which one happened at sunspot maxima and which at the minima, but there was a striking correlation.
Re:Cloud cover (Score:3, Interesting)
just having a hard time visualising that sometime in our evolutionary history there were some animals that didn't age.
They're called micro-organisms, although they don't exactly "not age". They reproduce by binary fission and therefore the offspring cells are nominally genetically identical to the parent. You can, if you like, say that one of them IS "the parent" (possibly with a bit of genetic modification) and the other is "the offspring." If you look at it that way (which admittedly takes a bit of squinting) their are single-celled organisms that around that are millions of years old (but genetically very different from their nominally identical selves of millions of years ago, due to those accumulated modifications.)
The GP's point is also not exactly correct: "competition" in the evolutionary sense doesn't happen between species. It happens between individuals of the same species. So a better way of putting the argument is: species with very long lifespans will be strongly selected for shorter lifespans when the rate of environmental change is high.
That is, the individuals who reproduce younger will have a larger chance of having offspring that are well-suited for the current environment, and those offspring will tend to reproduce younger as well, allowing the next generation's selective filtering (a nice euphemism for killing lots and lots of individuals) to operate rather more gently than on the offspring of individuals that reproduce later in life.
Age of first reproduction tends to be strongly anti-correlated with longevity. It's just like writing code under a tight deadline: the adaptations to get the job done fast tend to reduce maintainability, and it appears that the advantage of reaching the age of reproduction earlier and having a shorter reproductive lifespan is, in the typical environments found on Earth, more significant than building to last but not squeezing out those first pups for a couple of years after your contemporaries have.
If the Earth's environment were far more stable, species would be much longer lived. As it is, with significant natural climate variation on all timescales from decadal to milenial, a very long-lived species would have individuals adapted to one environment pushing out offspring in environments that they would be relatively ill-adapted for. There's very little selective advantage in that (although one could perhaps argue for the advantage of a really, really long-lived species that was able to wait it out until the next round of optimium conditions occurred. But there are some minima that even evolutionary algorithms have a hard time reaching.)